This invention relates generally to rotating machine technology and, specifically, to an attachment system for securing a ceramics matrix composite combustor liner to metal mounting attachments in a turbine combustor.
Advanced gas turbine engine development has suggested for use in high-temperature applications such as turbine combustor liners, certain non-metallic materials having higher temperature capability than the metal materials currently in use. One specific class of such non-metallic, low thermal expansion materials is ceramic matrix composite (CMC) materials which can operate at significantly higher temperatures than metals, and allow greatly reduced cooling requirements that can be translated into increased engine efficiency and output. With higher temperature capability, CMC materials can also simultaneously allow a reduction in combustor pressure drop by deleting conventional cooling enhancement features such as turbulators.
In order to realize the benefit of operating a gas turbine with a CMC liner, however, new methods of mounting CMC liners that accommodate the low coefficient of thermal expansion of the CMC material as well as the comparatively low strain-to-failure of CMC's relative to conventional metallic materials, must be developed. Thus, the challenge in using CMC materials for combustor liners is developing the interfaces to existing metal hardware in a cost-effective system that meets life and cost requirements.
For metal combustor liners, attachment components or features are readily joined to the metallic liner by brazing, welding, staking or other well-developed and reliable joining methods. Such attachment features typically provide support for cylindrical liners in the radial, axial and tangential directions.
For example, a typical three lug metal liner mounting arrangement provides for a radially floating design that semi-determinately captures three blocks on the metal liner into flow sleeve lugs. Forward axial loads from the combustor liner are reacted into the brazed blocks. With stack-up tolerances and forward to aft concentricity misalignment, this configuration could reasonably take all of the normal operating loads through a single lug. Examples of this technology may be seen in commonly owned U.S. Pat. Nos. 5,274,991; 5,323,600; 5,749,218; 6,279,313 and 6,216,442. These designs are not appropriate for CMC liners, however, because it is not feasible to braze or weld metal blocks to the CMC liner.
CMCs have mechanical properties that must be carefully considered during design and application of an article such as a combustor liner which interfaces with metallic hardware of significantly higher strength and higher thermal expansion characteristics. While some fastening techniques have been developed for securing CMC liners to metal components (See, for example, U.S. Pat. Nos. 6,904,757; 6,895,761; 6,895,757; 6,854,738 and 6,658,853.), there remains a need for a relatively simple but effective attachment system for CMC liners in gas turbine combustors.